Rear view mirror, rain sensor, and other brackets for mounting of such components conventionally have been bonded to the interior surface of automotive glass using films made of materials such as polyvinyl butyral (PVB), structural epoxy, and silicones.
These typical bonding materials are applied using conventional techniques and are known to have specific needs in terms of, for example, temperature and time to achieve cure and, hence, the requisite level of bond strength. It therefore in the past has been advantageous and commonplace in the automotive glass industry to apply such brackets at a stage in the glass lamination process that precedes the autoclaving process, as the vast majority of automotive laminated glass requires autoclaving as a part of the normal product flow. As is known, autoclaving involves processing at elevated temperatures and pressures. The adhesives used on the brackets thus may be cured to achieve the desired bond characteristics within the autoclave process, which occurs downstream of the initial application.
There is an ever-increasing trend today to add more sensors and brackets to automotive glass. These sensors oftentimes are added to the front windshield in the top central area. These sensors include items such as, for example, rear view mirrors, rain sensors, multifunction cameras, collision avoidance sensors, lane departure cameras, and the like. In an effort to consolidate these sensors, many automotive original equipment manufacturers (OEMs) have developed large brackets designed to accept the mounting of all of the sensors in one unit. The reasoning is that consolidating the plural sensors into one large bracket may help reduce (and possibly even completely avoid) the need to bond many separate entities and the concomitant need to deal with the tolerance stack-ups of all of the separate components.
The autoclaving process involves loading the glass components onto racks with an air separation between them to promote even heating. The process is executed as a batch, which helps increase the use of the interior space of the autoclave, e.g., towards a theoretical maximum capacity. Unfortunately, the advent of much larger bracketry to be attached to the glass causes the spacing between parts to be significantly enlarged, thereby reducing the density of parts in the autoclave for a given cycle and, in turn, resulting in a net reduction of process throughput. As autoclaves are a high capital cost item, it becomes clear that reducing the density of parts in a batch may result in a prohibitive cost increase to the product.
Because of this problem, the majority of these larger brackets are applied in dedicated assembly processes after autoclaving and during the final assembly of the glass component. The change in the process flow means that the same adhesive systems are no longer applicable, as one cannot duplicate the high temperature and high pressure conditions of the autoclave. Without this process, and for reasons specific to each adhesive, the required bond strength may not be achieved or the cure time may be excessively long and thus not effectively manageable within a high volume process.
These large brackets now are oftentimes applied with wet adhesive systems such as moisture cure polyurethane or two part reactive cure materials. Unfortunately, these materials generally do not have an immediate grip or “green strength” as applied so the brackets, have tight positional tolerances, must be either clamped during cure or secured temporarily by tapes over the top or in selected positions on the surface contacting the glass, etc. Furthermore, the additional tape steps cause added cost and have an inherent risk of placement slip of the component.
Thus, it will be appreciated that there is a need in the art for improved techniques for bonding automotive brackets for sensors, rear view mirrors, and/or other components to an interior surface of the glass, especially where large type brackets are involved.
Certain example embodiments of this invention relate to a method of bonding a bracket to a vehicle windshield. The bracket is applied to the vehicle windshield, with the bracket having a die-cut film-based adhesive pre-applied to one or more mating surfaces thereof. The film-based adhesive is allowed to cure at a temperature at or near ambient so as to bond the bracket to the vehicle windshield. The film-based adhesive has an immediate green strength adequate to fully locate the bracket during subsequent curing of the adhesive. The film-based adhesive on the bracket is applied to the vehicle windshield at a temperature at or near ambient.
Certain example embodiments of this invention relate to a method of bonding a bracket to a vehicle windshield. The bracket supports a rear view mirror and/or one or more sensors. The bracket is applied to the vehicle windshield, with the bracket having a die-cut film-based adhesive pre-applied to each of a plurality of spaced apart mating surfaces thereof. The film-based adhesive is allowed to cure so as to bond the bracket to the vehicle windshield, with any curing being completed to a desired strength level within 72 hours. The film-based adhesive on the bracket is applied to the vehicle windshield and allowed to cure at a temperature at or near ambient. The film-based adhesive has an immediate green strength adequate to fully locate the bracket during subsequent curing of the adhesive.
Certain example embodiments of this invention relate to a system for bonding a bracket to a vehicle windshield. The bracket supports a rear view mirror and/or one or more sensors. The bracket is applied to the vehicle windshield at a temperature at or near ambient via a die-cut film-based adhesive pre-applied to each of a plurality of spaced apart mating surfaces thereof. The film-based adhesive is curable to a desired strength level at a temperature at or near ambient within 72 hours of application to the vehicle windshield. The film-based adhesive has an immediate green strength adequate to fully locate the bracket during subsequent curing of the adhesive.
According to certain example embodiments, the film-based adhesive is an epoxy-based film that, prior to said applying, is to be stored in a refrigerated condition to retard curing. The epoxy-based film is blanked in a cold state to the bracket prior to said applying. A cure cycle of the epoxy-based film is activatable by warming the epoxy-based film to ambient temperature. The bracket and/or vehicle windshield is warmed to ambient temperature or a temperature slightly higher than ambient temperature prior to application.
According to certain example embodiments, the film-based adhesive is a moisture cured urethane based film that, prior to said applying, is to be stored in a dry environment. The moisture cured urethane based film includes a tacky surface to promote initial adhesion upon contact. After application, the moisture cured urethane based film is exposed to an elevated humidity to promote curing.
According to certain example embodiments, the film-based adhesive is a urethane adhesive film such as that typically used to laminate glass to polycarbonate. The urethane adhesive film is activatable or bondable at temperatures only slightly above ambient. The film-based adhesive is cured to a strength level adequate to meet operational specifications for the component in under 72 hours.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.